1. Field of the Invention
The present invention generally relates to a method of manufacturing a semiconductor device. More specifically, the present invention relates to a method of manufacturing a semiconductor device that includes a ferroelectric capacitor.
2. Background Information
Conventional semiconductor memories that use ferroelectrics as capacity insulators of capacitors are disclosed in Japanese Patent Application Laid Open No. H05-299610, especially pp. 8-10, FIGS. 20 and 83 (hereinafter reference 1), Japanese Patent Application Laid Open No. H09-266200, especially pp. 3-4, FIG. 1 (hereinafter reference 2), and Japanese Patent Application Laid Open No. H09-251983, especially pp. 2-3, FIGS. 1 and 2 (hereinafter reference 3), for instance. Japanese Patent Application Laid Open Nos. H05-299610, H09-266200, and H09-251983 are hereby incorporated by reference.
The reference 1 discloses an etching method of a laminated structure film that is provided with a plug electrode, a lower electrode, a ferroelectric film, and an upper electrode. The plug electrode, the lower electrode, the ferroelectric film, and the upper electrode are sequentially formed and then dry-etched in the block using a resist as a mask. Here, the plug electrode is made of a titanium nitride (TiN) film that is formed on a surface of an insulation film while also being embedded in an aperture formed in the insulation film. The lower electrode is made of platinum (Pt), the ferroelectric film is made of a PZT (lead titanate-lead zirconate:PbTiO3—PbZrO3). Further, the upper electrode is made of Pt, TiN, tungsten (W), aluminum (Al), or the like. In this method, by embedding the TiN film in the aperture of the insulation film while also forming the TiN film on the surface of the insulation film, the lower electrode, the ferroelectric film, and the upper electrode can be made flat. Thereby, the interval between the upper electrode and the lower electrode can be maintained at a predetermined distance, due to which flowing of leak current between the upper electrode and the lower electrode can be prevented.
The reference 2 discloses an etching method of a laminated structure film that is provided with an under layer Pt electrode, a ferroelectric film, an upper layer Pt electrode, and a titanium (Ti) film. The under layer Pt electrode, the ferroelectric film, the upper layer Pt electrode, and the Ti film are sequentially formed, and the Ti film is patterned into a predetermined pattern. Then, using the patterned Ti film as a mask, the under layer Pt electrode, the ferroelectric film, the upper layer Pt electrode, and the Ti film are continuously dry-etched in the block by a dry etching method that uses a plasma of mixed gas including Cl2 and O2. In etching the laminated structure film, by using the Ti film, which can be easily oxidized, as the etching mask, the etching rate becomes slow due to the oxidization of the Ti film. On the other hand, the etching rate with respect to the etching subject films (i.e. the under layer platinum electrode, the ferroelectric film, and the upper layer platinum film) can be sufficiently secured, and thereby, the selection ratio between the etching subject films and the etching mask can be enlarged. By this arrangement, processing accuracy can be improved.
The reference 3 discloses an etching method of a laminated structure film that is provided with a lower electrode made of an Ir/IrO2 film, a PZT film and an upper electrode made of an Ir/IrO2 film. In this etching method, the PZT film is dry-etched using mixed gas including BCl3 and Cl2. By this arrangement, it is possible to prevent possible removal of a desired substance from the etching surface. Moreover, for the dry etching of Ir/IrO2, by using the mixed gas of BCl3 and Cl2 where fluoride is being added, it is possible to prevent Ir from being reattached to a side wall of a resist.
However, with regards to the etching methods of the references 1 and 2, in a method of manufacturing a capacitor by processing a laminated structure film made of an upper electrode, a ferroelectric film, and a lower electrode in the block, a damaged layer may be formed in the ferroelectric film. This damaged layer is formed by Cl2 having a reducing nature when the ferroelectric film and/or the lower electrode are dry-etched. The damaged layer is formed in a way that advances inside the ferroelectric film from the side of the ferroelectric film that is exposed after the processing. In the damaged layer, the original dielectric polarization property of the ferroelectric film can be lost, or the damaged layer can turn to a path that allows current leak from the upper electrode to the lower electrode. As a result, there is a possibility that effective polarization properties may not be acquired with respect to the capacitor area. Even with a capacitor of small area or a capacitor of large area, a damaged layer is formed approximately in the same size. Therefore, especially when the area of the capacitor becomes smaller, the rate of the area occupied with the damaged layer becomes larger with respect to the effective area of the capacitor, and this allows characteristic degradation such as degradation of dielectric polarization properties, increase in current leaks, etc. to occur easily. Therefore, when it comes to a ferroelectric capacitor that is miniaturized for high integration, the rate of the area occupied with the damaged layer with respect to the effective area of the capacitor will become much larger, and it is considered that the problems of degradation of dielectric polarization properties and increases in current leaks will become more apparent.
Incidently, the reference 3 does not mention any problem that can be caused by dry-etching the laminated structure film in the block in forming the ferroelectric capacitor.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved method of manufacturing a semiconductor device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.